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ALDBOROUGH. urns, and coins have been found in great number. Pop., 1001, 800.

ALDEB'ARAN (Ar. al-dabaran, the follower, i.e., of the Pleiades). The name of a star of the first magnitude, in the constellation Taurus. It is the largest and most brilliant of a cluster of five which the Greeks called the Hyades. From its position it is sometimes termed "the bull's eye."

ALDEGONDE, al'de-goNd', See.

ALDEGREVER, jll'dcgra'ver, Heinrich (1502-c. 1562). A German painter and engraver. From his style, which closely resembles his mas- ter's, he has been called "the Albrecht Dürer of Westphalia." His engravings put him in the first rank of "little masters." They include por- traits of Luther, Melanchthon, and John of Ley- den. Of his paintings, the most noteworthy are the "Portrait of a Young Man" (1544), at Vi- enna, and a "Resurrection," at Prague.

AL'DEHYDE, Acetic, CH,CH0, often called Ordinary Aldehyde, or simply Aldehyde. A colorless liquid having a peculiar pungent and suffocating odor. It is very volatile and inflam- mable; it boils at 20.8° C, and has at 0° C. a specific gravity 0.801. It occurs in crude alcohol and wood spirit, and is readily made from ordinary alcohol by oxidation with chromic acid. If a mixture of three parts of alcohol and four parts concentrated sulphuric acid is run into a vessel kept in a warm water-bath and contain- ing three parts of coarsely powdered potassium bi- chromate and twelve parts water, a reaction takes place, during which a considerable amount of aldehyde is formed. The latter is isolated in a somewhat impure state by distillation, and may be purified by the use of ammonia. Alde- hyde combines with ammonia to form a solid crvstalline substance called aldehyde-ammonia, aiid having the formula CH.CH (NH,) OH; alco- hol and acetal, which are generally contained as impurities in crude aldehyde, form no solid compound •nith ammonia. Therefore, to separate aldehyde from these substances, crystalline al- dehyde-ammonia is produced by the direct action of ammonia, washed with ether, and broken up by distillation with dilute sulphuric acid. The aldehyde thus obtained is further dehydrated by distillation with dry calcium chloride. Aldehyde is used in the manufacture of certain valuable dyes. If added to an ammoniacal solution of sil- ver nitrate, it produces a precipitate of metallic silver, which may form a mirror if evenly de- posited on a glass surface. By the action of re- ducing agents, aldehyde is converted into alco- hol; oxidizing agents convert it into acetic acid. If a drop of strong sulphuric acid is added to aldehyde, the latter is transformed into paralde- hyde, a colorless, transparent liquid having the molecular formula C,;H,,03; it has a strong char- acteristic odor and a somewhat burning taste; if cooled below 0° C, it solidifies, form- ing crystals which melt at 10.5° C. Paralde- hyde is moderately soluble in water, its solubil- ity decreasing with an increase of temperature. If taken internally in doses of from one to four cubic centimeters, paraldehyde produces sleep without affecting the heart; it is, therefore, used as a substitute for chloral. Though it has the dis- agreeable effect of imparting a persistent and offensive odor to the breath. Paraldehyde may be readily reconverted into aldehyde by distilling

with dilute sulphuric acid. By the action of acids on aldehyde at a low temperature, another compound having the same percentage composition as aldehyde is obtained; this compound is called metaldehyde; it is colorless, crystalline, insoluble in water, and is readily converted into aldehyde by heating with dilute acids. Aldeliyde was first isolated and studied by Liebig in 1835.

ALDEHYDES (clipped form of aicohol de7ti/(irogenatum, alcohol deprived of hydrogen). An important class of organic chemical compounds characterized by the group CHO. The aldehydes are derived from the primary alcohols (see ) by removing part of the hydrogen of the latter by means of an oxidizing agent. Thus, when ethyl alcohol is oxidized with aqueous chromic acid, ordinary aldehyde is produced according to the following chemical equation:

CHjCH.OH + = CHjCHO + H,0 Ethyl alcohol AUlchyiie

Most of the aldehydes are volatile liquid compounds, and are readily converted by oxidizing agents into the corresponding organic acids. Thus benzaldehyde (benzoic aldehyde) is readily oxidized to benzoic acid, according to the following equation:

CeH.CHO -f = CaH.COOH Benzaldehyde Benzoic acid

The aldehydes react with a great variety of substances, and by the use of them chemists have been able to obtain a large number of valuable organic compounds. Among the characteristic reactions of the aldehydes may be mentioned the following:

1. Being powerful reducing agents, the aldehydes form a mirror of metallic silver when heated in a glass vessel with an ammoniacal solution of silver nitrate to which some caustic soda has been added.

2. By the action of phosphorus pentachloride, the oxygen atom of the aldehyde group (CHO) is replaced by two atoms of chlorine. Thus, by the action of phosphorus pentachloride upon or- dinary aldehyde, ethylidene chloride may be ob- tained according to the following equation:

CHjCHCL -f POCI3 CHjCHO -f PCI, Aldehyde Ethylidene chloride

It will be remembered that by the same reagent the hydroxyl group OH of alcohols and acids is replaced by one atom of chlorine. Thus ordinary alcohol is transformed into ethyl chloride, accord- ing to the following equation:

C,H,OH + PCI, = C,H,C1 -f POCI3 -f HOI Ethyl alcohol Ethyl chloride

3. The aldehydes combine with alcohols to form compounds called acetals. Thus, ordinary acetal may be obtained according to the following equation:

CH3CHO 4- 2C2H5OH = UH3Ch/2^=][^5 + H^O Aldehyde Alcohol Acetal

4. The presence of an aldehyde in a sample submitted for examination (or the presence of the aldehyde group CHO in a compound) may be demonstrated by adding the substance to a so- lution of a rosanilin salt that has been bleached by sulphurous acid (SOj): the appearance of a